1. Field of the Invention
The present invention relates to a method for determining a transmission path of a router system, and more particularly to a method for determining an efficient packet-transmission path of a router system in a multicast operation.
2. Description of the Related Art
FIG. 1 is a schematic block diagram of a router system. The router system includes a routing processor (RP) 100, at least one linecard processor (LP) 200 provided with a port to be connected to a network or a host and functioning as an external interface, and a switch (SW) 300 setting a packet transmission path under control of the routing processor (RP) 100. The routing processor (RP) uses a forwarding table to set the transmission path when transmitting packets.
Referring to FIG. 2, a conventional forwarding table includes an Internet Protocol (IP) address, a media access control (MAC) address, and a physical port.
FIG. 3 is a flowchart illustrating a procedure for determining a transmission path of a conventional router system. In packet transmission, the routing processor (RP), which is responsible for general routing control in the router system, retrieves a destination address with reference to the forwarding table at operation S110. Here, the destination address can be retrieved by comparing with the IP address or the MAC address in the forwarding table shown in FIG. 2.
If the destination address is not retrieved at operation S110, the routing processor (RP) records the destination address in the forwarding table at operation S210, and sets a default physical port as a transmission path to transmit a packet at operation S220. On the other hand, if the destination address is retrieved at operation S110, the routing processor (RP) sets the physical port, which corresponds to the destination address recorded on the forwarding table, as the transmission path to transmit the packet at operation S310.
Such a conventional method for determining the transmission path of the router system is easy to manage and operate. However, the conventional method has difficulty in instantly coping with and supplementing traffic congestion, which may occur in a certain port, since it is necessary to change the port in the forwarding table in order to perform load-balancing in the event that traffic congestion occurs on the port. In other words, since the router system needs to stop operations of the higher routing/forwarding processors before changing the port in order to change the forwarding table occupied by higher routing/forwarding processors, the changeover operation is not easy.
Furthermore, in a multicast operation, if the router system contains no forwarding table for supporting multicasting, an extra forwarding engine for multicasting needs to be provided in the forwarding table and each port needs to have a forwarding table record. In the case where the router system has 32 ports which are destination ports for packet transmission, the corresponding multicast addresses need to have 32 forwarding table records.
However, in multicast communication where session participants (subscribers) frequently join and withdraw, the router system experiences a heavy load because the forwarding table record has to be changed accordingly.